Variable pitch for coordinated control

ABSTRACT

A system is described that includes a turbine engine including an engine fan including one or more variable-pitch blades driven by a shaft, which rotates at a rotational speed which depends on a pitch of the one or more variable-pitch blades of the engine fan. The system further includes a generator configured to produce alternating-current (AC) electricity at a particular frequency relative to the rotational speed of the shaft. The system also includes a propulsor, which includes a propulsor motor and a propulsor fan. The propulsor motor is configured to drive, based on the AC electricity produced by the generator, the propulsor fan. The system includes a controller configured to control the particular frequency of the AC electricity by at least controlling the pitch of the one or more variable-pitch blades of the engine fan and thereby the rotational speed of the generator.

This application is a continuation of U.S. application Ser. No.15/371,757, filed Dec. 7, 2016, which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

This disclosure relates to distributed propulsion systems.

BACKGROUND

A turbine engine is a type of combustion system that may be used topower a system such as an aircraft, other moving vehicles, or anelectric generator. The turbine engine may be configured to rotate ashaft. The turbine engine may be configured to rotate the shaft to drivean electric generator that is configured to produce electricity based onthe rotation of the shaft. An electrical bus may deliver the electricityproduced by the generator to a motor, such as a propulsor motor thatdrives a fan used for propulsion.

SUMMARY

In some examples, the disclosure describes a system that includes aturbine engine including an engine fan including one or morevariable-pitch blades driven by a shaft which rotates at a rotationalspeed which depends on a pitch of the one or more variable-pitch blades.The system further includes a generator configured to producealternating-current (AC) electricity at a particular frequency relativeto the rotational speed of the shaft. The system further includes apropulsor which includes a propulsor motor and a propulsor fan. Thepropulsor motor is configured to drive the propulsor fan, based on theAC electricity produced by the generator. The system includes acontroller configured to control the particular frequency of the ACelectricity by at least controlling the pitch of the one or morevariable-pitch blades of the engine fan and thereby the rotational speedof the generator.

In some examples, the disclosure describes a method for generatingpropulsion, the method including determining a propulsion for apropulsion fan driven by a propulsor motor based on a particularfrequency of alternating-current (AC) electricity; determining a pitchof one or more variable-pitch blades of an engine fan of a turbineengine to cause a shaft of the turbine engine to rotate at a rotationalspeed to cause a generator to produce the particular frequency of ACelectricity; and controlling the pitch of the one or more variable-pitchblades to cause the generator to produce the AC electricity at theparticular frequency and the propulsor motor to drive the propulsor fanto generate the propulsion based on the AC electricity.

In some examples, the disclosure describes a system including a firstturbine engine including a first engine fan including one or morevariable-pitch blades driven by a first shaft which rotates at a speedwhich depends on a pitch of the one or more variable-pitch blades of thefirst engine fan. The system also includes a first generator configuredto produce, based on a rotation of the first shaft, firstalternating-current (AC) electricity at a first frequency relative tothe rotational speed of the first shaft. The system further includes asecond turbine engine including a second engine fan including one ormore variable-pitch blades driven by a second shaft which rotates at aspeed which depends on a pitch of the one or more variable-pitch bladesof the second engine fan. The system may also include a second generatorconfigured to produce second alternating-current (AC) electricity at asecond frequency relative to the rotational speed of the second shaft.The system further includes a propulsor including a propulsor fan and apropulsor motor configured to drive the propulsor fan, selectively basedon the first AC electricity produced by the first generator or thesecond AC electricity produced by the second generator.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual block diagram illustrating a synchronousalternating-current (AC) electrical system including a variable-pitchturbine engine and a propulsor motor that drives a propulsor fan basedon the AC electricity produced by a generator connected to the turbineengine, in accordance with one or more techniques of this disclosure.

FIG. 2 is a conceptual block diagram illustrating a synchronous ACelectrical system including two variable-pitch turbine engines, twogenerators, two propulsors, and a reconfiguration element configured toselectively transmit AC electricity from the two generators to twopropulsor motors, in accordance with one or more techniques of thisdisclosure.

FIG. 3 is a drawing illustrating two turbine engines, two generators, apropulsor system, and a reconfiguration element, in accordance with oneor more techniques of this disclosure.

FIGS. 4A-4G are diagrams illustrating reconfiguration elementsconfigured to selectively transmit AC electricity from two generators totwo propulsors, in accordance with one or more techniques of thisdisclosure.

FIGS. 5A-5C are diagrams illustrating reconfiguration elementsconfigured to selectively transmit AC electricity from two generators totwo propulsors, in accordance with one or more techniques of thisdisclosure.

FIGS. 6-8 are conceptual block diagrams illustrating engine core speedcontrol loops with combinations of fixed and variable pitch engine fansand propulsor fans, in accordance with one or more techniques of thisdisclosure.

FIGS. 9-11 are conceptual block diagrams illustrating enginelow-pressure speed control loops with combinations of fixed and variablepitch engine fans and propulsor fans, in accordance with one or moretechniques of this disclosure.

FIG. 12 is a flowchart illustrating an example process implemented by asystem including a variable-pitch turbine engine, in accordance with oneor more techniques of this disclosure.

DETAILED DESCRIPTION

In general, this disclosure describes techniques for implementing anexample synchronous alternating-current (AC) electrical system thatincludes a turbine engine with a variable-pitch engine fan and isconfigured to adjust the pitch of the variable-pitch blades to (at leastpartially) control the rotational speed of a shaft of the turbineengine. A generator of the example system is coupled to the shaft andproduces AC electricity that has a frequency that is based on therotational speed of the shaft. The example system includes a propulsormotor that drives a propulsor fan based on the AC electricity producedby the generator and the example system may control the rotational speedof the shaft and the amount of propulsion generated by the propulsor fanby adjusting the by adjusting the pitch of the variable-pitch blades. Inother words, by adjusting the pitch of the variable-pitch blades of theengine fan, the example system may control the frequency of the ACelectricity that is driving the propulsor fan to affect the rotationalspeed of the propulsor fan and thereby the amount of propulsionproduced. In this way, the amount of propulsion generated by thepropulsor fan may be based on the frequency of the AC electricityproduced by the generator, which may be based on the pitch of thevariable-pitch blades of the engine fan.

FIG. 1 is a conceptual block diagram illustrating a synchronousalternating-current (AC) electrical system 2 including a variable-pitchturbine engine 4 and a propulsor motor 16 that drives a propulsor fan 18based on the AC electricity 14 produced by a generator 12 connected tothe turbine engine 4, in accordance with one or more techniques of thisdisclosure. Synchronous AC electrical system 2 may be configured todeliver AC electricity 14 to propulsor 15, where propulsor motor 16 maydrive propulsor fan 18. The propulsion created by propulsor fan 18 maybe used in a variety of ways or for a variety of systems andapplications (e.g., aircraft, locomotives, watercraft, power plants,electric generators, and any or all other systems and applications thatrely on mechanical energy from a turbine engine to perform work).

Turbine engine 4 is configured to rotate shaft 10. Turbine engine 4 mayinclude engine fan 7 with variable-pitch blades 8A-8N, at least aportion of shaft 10, and additional components necessary to rotate shaft10 that are not shown in FIG. 1. In some examples, turbine engine 4 mayinclude generator 12, and generator 12 may be positioned inside ofturbine engine 4. In other examples, generator 12 may be separate fromturbine engine 4 and generator 4 may be positioned outside of turbineengine 4. Turbine engine 4 may be a gas turbine engine, a nuclearturbine engine, a steam turbine engine, or any other suitable turbineengine.

Variable-pitch blades 8A-8N of engine fan 7 are configured to rotatebased on the fluid passing through turbine engine 4 and furtherconfigured to cause shaft 10 to rotate based on the movement of fluidthrough turbine engine 4. Engine fan 7 may be mechanically connected toshaft 10, and shaft 10 of turbine engine 4 may drive engine fan 7 andgenerator 12. Variable-pitch blades 8A-8N may include an adjustablepitch mechanism such that a pitch of variable-pitch blades 8A-8Ndetermines the speed of rotation of shaft 10. A decrease of the pitch ofvariable-pitch blades 8A-8N may cause shaft 10 to rotate faster, whilean increase of the pitch of variable-pitch blades 8A-8N may cause shaft10 to rotate slower. For example, a flat pitch on variable-pitch blades8A-8N may cause shaft 10 to rotate at a high speed for a fixed-powerfan.

Shaft 10 is configured to rotate based on mechanical energy from turbineengine 4 and is further configured to rotate based on the pitch ofvariable-pitch blades 8A-8N. In other words, shaft 10 may rotate at arotational speed, which depends on a pitch of variable-pitch blades8A-8N. Shaft 10 may be connected to generator 12 such that shaft 10drives a rotor in generator 12. Shaft 10 may include a low-pressure (LP)shaft, a high-pressure (HP) shaft, or an auxiliary shaft that is drivenby the LP shaft or the HP shaft. The core power of turbine engine 4 maydrive the rotation of shaft 10.

Generator 12 is configured to convert mechanical power derived fromshaft 10 to electrical power for use by other components or circuits.Generator 12 may be an AC generator such as an induction generator.Generator 12 may be configured to produce AC electricity 14 at aparticular frequency based on a rotation of shaft 10. In other words,the particular frequency of AC electricity 14 may be relative to therotational speed of shaft 10 and based on the speed of engine fan 7.Generator 12 may include a wound field machine, a Halbach arraygenerator with permanent magnets on a rotor that is driven by shaft 10,or any other type of generator. In some examples, generator 12 may beintegrated into turbine engine 4 and driven by an LP shaft.

Propulsor 15 includes propulsor motor 16 and propulsor fan 18. Propulsormotor 16 is configured to drive propulsor fan 18 based on AC electricity14 produced by generator 12. Synchronous AC electrical system 2 maytransmit AC electricity 14 from generator 12 to propulsor motor 16. ACelectricity 14 may have a single phase or multiple phases, such asthree-phase AC electricity. Propulsor motor 16 may be configured toconvert electrical energy to mechanical energy to drive propulsor fan18. The terms “electrical power” and “mechanical power” may refer torates of consuming or generating electrical energy or mechanical energy.

Propulsor fan 18 is configured to be driven by propulsor motor 16 togenerate propulsion based on the mechanical power produced by propulsormotor 16. Propulsor fan 18 may be remote from turbine engine 4. Forexample, propulsor fan 18 may be positioned on a wing of an aircraftwhereas turbine engine 4 may be positioned at or near a fuselage of theaircraft. Propulsor fan 18 may include a boundary layer ingestion (BLI)fan configured to activate the boundary layer of a vehicle. Propulsorfan 18 may include a partially distributed propulsion system, awing-embedded fan, a blown-wing fan, a wing-tip fan, a surface-mountedBLI fan, and/or any other suitable fan and/or propulsor.

Controller 20 is configured to control the pitch of variable-pitchblades 8A-8N of turbine engine 4 by sending a command to avariable-pitch unit (not shown in FIG. 1). The variable-pitch unit maybe configured to adjust the pitch of variable-pitch blades 8A-8N basedon the command from controller 20. Controller 20 may monitor theparticular frequency of AC electricity 14, and controller 20 may beconfigured to control the particular frequency of AC electricity 14 bycontrolling the pitch of variable-pitch blades 8A-8N. Controller 20 maybe configured to control the propulsion generated by propulsor fan 18 bycontrolling the pitch of variable-pitch blades 8A-8N. Controller 20 mayalso control the rotational speed of generator 12 by controlling thepitch of variable-pitch blades 8A-8N. In some examples, propulsor fan 18may include one or more variable-pitch blades, and controller 20 may beconfigured to control the propulsion generated by propulsor fan 18 bycontrolling the pitch of the one or more variable-pitch blades ofpropulsor fan 18.

Controller 20 may include any suitable arrangement of hardware,software, firmware, or any combination thereof, to perform thetechniques attributed to controller 20 herein. Examples of controller 20include any one or more microprocessors, digital signal processors(DSPs), application specific integrated circuits (ASICs), fieldprogrammable gate arrays (FPGAs), or any other equivalent integrated ordiscrete logic circuitry, as well as any combinations of suchcomponents. When controller 20 includes software or firmware, controller20 further includes any necessary hardware for storing and executing thesoftware or firmware, such as one or more processors or processingunits.

In general, a processing unit may include one or more microprocessors,DSPs, ASICs, FPGAs, or any other equivalent integrated or discrete logiccircuitry, as well as any combinations of such components. Although notshown in FIG. 1, controller 20 may include a memory configured to storedata. The memory may include any volatile or non-volatile media, such asa random access memory (RAM), read only memory (ROM), non-volatile RAM(NVRAM), electrically erasable programmable ROM (EEPROM), flash memory,and the like. In some examples, the memory may be external to controller20 (e.g., may be external to a package in which controller 20 ishoused).

Although controller 20 is generally described as being the primary unitfor controlling each of the components of synchronous AC electricalsystem 2 for performing the techniques described herein, in someexamples, the individual components of synchronous AC electrical system2 may include additional functionality for performing some or all of theoperations described below with respect to controller 20. For example, acombination of one or more of turbine engine 4, generator 12, propulsormotor 16, and propulsor fan 18 may include components for controllingthe generation, transmission, and use of AC electricity in synchronousAC electrical system 2.

In accordance with the techniques of this disclosure, propulsor motor 16may drive propulsor fan 18 based on AC electricity 14 produced bygenerator 12. The particular frequency of AC electricity 14 may be basedon the rotation of shaft 10. The speed of the rotation of shaft 10 maybe based on the pitch of variable-pitch blades 8A-8N. Synchronous ACelectrical system 2 may control the amount of propulsion generated bypropulsor fan 18 by controlling the pitch of variable-pitch blades 8A-8Nand by throttling turbine engine 4. The propulsion generated bypropulsor fan 18 may be independent of the thrust produced by turbineengine 4. In some examples, the ratio of the rotational speed rotationalspeed of propulsor fan 18 and the rotational speed of shaft 10 may be aconstant value.

As compared to a non-synchronous electrical system, synchronous ACelectrical system 2 may include fewer or no power electronics conversioncircuits. By reducing or eliminating power electronics, the synchronousAC electrical system may have reduced weight, cost, and maintenance.Synchronous AC electrical system 2 may include additional benefits suchas relative simplicity of controlling the particular frequency of ACelectricity 14 and relative simplicity of controlling the propulsiongenerated by propulsor fan 18. A non-synchronous electrical system maycontrol the frequency of AC electricity produced by a generator bythrottling the speed of a turbine engine and/or through an AC/AC powerconverter electrically connected to a generator. Controller 20 maycontrol the particular frequency of AC electricity 14 by controlling thepitch of variable-pitch blades 8A-8N.

A non-synchronous electrical system may control the propulsion generatedby a propulsor by throttling the speed of a turbine engine, through apower converter electrically connected to a generator, and/or through apower converter electrically connected to a propulsor motor configuredto drive the propulsor fan. Controller 20 may control the propulsiongenerated by Propulsor fan 18 by controlling the pitch of variable-pitchblades 8A-8N.

FIG. 2 is a conceptual block diagram illustrating a synchronous ACelectrical system 30 including two turbine engines 34A, 34B withvariable-pitch engine fans 36A, 36B, two generators 42A, 42B, twopropulsors 43A, 43B, and a reconfiguration element 48 configured toselectively transmit AC electricity from the two generators to twopropulsor motors 44A, 44B, in accordance with one or more techniques ofthis disclosure. Through reconfiguration element 48, synchronous ACelectrical system 30 may be configured to selectively deliver electricalpower to one or both of propulsor motors 44A, 44B, where propulsor motor44A may drive propulsor fan 46A and propulsor motor 44B may drivepropulsor fan 46B.

Reconfiguration element 48 is configured to selectively transmit ACelectricity produced by generator 42A to zero, one, or both of propulsormotors 44A, 44B. Reconfiguration element 48 is also configured toselectively transmit AC electricity produced by generator 42B to zero,one, or both of propulsor motors 44A, 44B. Reconfiguration element 48may include one or more switches, such as metal-oxide semiconductorfield-effect transistors (MOSFETs), insulated-gate bipolar transistors(IGBTs), mechanical interrupters, and/or any other suitable switches.

Controller 50 is configured to control the pitch of variable-pitchblades 38 of engine fan 36A and the pitch of variable-pitch blades 39 ofengine fan 36B. Controller 50 may determine the pitch of variable-pitchblades 38 and/or the pitch of variable-pitch blades 39 to cause one orboth of shafts 40A, 40B to rotate at a rotational speed to cause one orboth of generators 42A, 42B to produce AC electricity at desiredfrequency. Controller 50 may be configured to selectively causereconfiguration element 48 to transmit the AC electricity produced bygenerator 42A to zero, one, or both of propulsor motors 44A, 44B.Controller 50 may be configured to selectively cause reconfigurationelement 48 to transmit the AC electricity produced by generator 42B tozero, one, or both of propulsor motors 44A, 44B.

In some examples, one or both of propulsor fans 46A, 46B may includevariable-pitch blades. Controller 50 may be configured to adjust thepitch of the variable-pitch blades of propulsor fan 46A and/or the pitchof the variable-pitch blades of propulsor fan 46B. By adjusting thepitch of the variable-pitch blades of one or both of propulsor fans 46A,46B, controller 50 may control the amount of propulsion generated bypropulsor fans 46A, 46B.

FIG. 3 is a drawing illustrating two turbine engines 64A, 64B, twogenerators 72A, 72B, propulsor system 82, and a reconfiguration element78, in accordance with one or more techniques of this disclosure.Turbine engine 64A may include variable-pitch unit 66A for controllingthe pitch of variable-pitch blades 68A, 68B. Variable-pitch unit 66A mayinclude a gearbox that is mechanically coupled to variable-pitch blades68A, 68B.

Shaft 70A may be configured to rotate based on the power provided by thecore to the LP turbine as well as the pitch of variable-pitch blades68A, 68B. Generator 72A may be configured to produce a first ACelectricity at a first frequency based on the rotational speed of shaft70A. Electrical bus 62A may be configured to transmit the first ACelectricity produced by generator 72A to reconfiguration element 78. Ina similar manner, turbine engine 64B may include may includevariable-pitch unit 66B for controlling the pitch of variable-pitchblades 69A, 69B. Generator 72B may be configured to produce a second ACelectricity at a second frequency based on the rotational speed of shaft70B, which may be based on the pitch of variable-pitch blades 69A, 69B.Electrical bus 62B may be configured to transmit the second ACelectricity produced by generator 72B to reconfiguration element 78.

Reconfiguration element 78 may be configured to selectively transmit thefirst AC electricity and the first AC electricity produced by generator72A to zero, one, or both of propulsor motors 74A, 74B. Reconfigurationelement 78 may also be configured to selectively transmit the second ACelectricity produced by generator 72B to zero, one, or both of propulsormotors 74A, 74B. Reconfiguration element 78 may include one or moreswitches for directing the first AC electricity and the second ACelectricity to propulsor system 82.

Propulsor system 82 may include propulsor fans 76A, 76B, each of whichmay include two or more blades. In some examples, the blades ofpropulsor fans 76A, 76B may include variable-pitch blades. Propulsorsystem 82 may include may include variable-pitch units 84A, 84B forcontrolling the pitch of the variable-pitch blades of propulsor fans76A, 76B. Each of variable-pitch units 84A, 84B may include a gearboxthat is mechanically coupled to the variable-pitch blades of propulsorfans 76A, 76B. If propulsor fans 76A, 76B include variable-pitch blades,a controller of synchronous AC electrical system 60 may have increasedindependence in controlling the thrust provided by the propulsor fans76A, 76B. Variable-pitch blades may also enhance the ability of windmillresynchronization of propulsor fans 76A, 76B.

Propulsor system 82 may include a two-stage fan system, where each ofpropulsor fans 76A, 76B are a fan stage of propulsor system 82.Reconfiguration element 78 may deliver the first AC electricity to oneof propulsor motors 74A, 74B and the second AC electricity to the otherof propulsor motors 74A, 74B. Thus, synchronous AC electrical system 60may not phase lock the first AC electricity and the second electricity.The speeds of turbine engines 64A, 64B may be managed independently by acontroller of synchronous AC electrical system 60, where each of turbineengines 64A, 64B drives a separate propulsor of propulsor fans 76A, 76B.

In some examples, propulsor system 82 may include a counter-rotatingairfoil rimmed fan system. If propulsor fans 76A, 76B include BLI fans,a counter-rotating airfoil rimmed fans may allow a relatively largestream tube to be captured by each of propulsor fans 76A, 76B. Ifpropulsor fans 76A, 76B capture a large stream tube of fluid, propulsorfans 76A, 76B may have greater impact on the boundary layer.

Controller 80 may be configured to control the pitch of variable-pitchblades 68A, 68B of turbine engine 64A by sending a command tovariable-pitch unit 66A. Controller 80 may be configured to control thepitch of variable-pitch blades 69A, 69B of turbine engine 64B by sendinga command to variable-pitch unit 66B. Variable-pitch unit 66A, 66B maybe configured to adjust the pitch of variable-pitch blades 68A, 68B,69A, 69B based on the command from controller 80. Controller 80 maymonitor the frequencies of the AC electricity produced by generators72A, 72B, and controller 80 may be configured to control the frequenciesof the AC electricity by controlling the pitch of variable-pitch blades68A, 68B, 69A, 69B. Controller 80 may be configured to control thepropulsion generated by propulsor fans 76A, 76B by controlling the pitchof variable-pitch blades 68A, 68B, 69A, 69B. In some examples, propulsorfans 76A, 76B may include one or more variable-pitch blades, andcontroller 80 may be configured to control the propulsion generated bypropulsor fans 76A, 76B by controlling the pitch of the one or morevariable-pitch blades of propulsor fans 76A, 76B.

In some examples, controller 80 may be configured to control the pitchof variable-pitch blades on propulsor fans 76A, 76B. By increasing thepitch of the variable-pitch blades on propulsor fans 76A, 76B,controller 80 may increase the load on generators 72A, 72B and reducethe speed of shafts 70A, 70B. A lower speed for shafts 70A, 70B may leadto a lower thrust for turbine engines 64A, 64B.

In some examples, a controller of synchronous AC electrical system 60may phase-lock the first AC electricity and the second AC electricity.The controller may control the frequency and phase of the first ACelectricity by controlling the pitch of variable-pitch blades 68A, 68Bthrough variable-pitch unit 66A. The controller may control thefrequency and phase of the second AC electricity by controlling thepitch of variable-pitch blades 69A, 69B through variable-pitch unit 66B.The controller may cause the frequency of the first AC electricity to beequal to frequency of the second AC electricity. The frequencies may bedefined as equal if the difference between the frequencies is less thana threshold percentage, such as one percent, five percent, ten percent,or any other suitable percentage. The controller may cause the phase ofthe first AC electricity to be equal to phase of the second ACelectricity. The phases may be defined as equal if the differencebetween the phases is less than five degrees or less than some othertolerable difference in degree value. Accordingly, this would cause thespeeds of the gas turbines to be phase locked. By controlling thecomponents of synchronous AC electrical system 60, controller 80 maycontrol the propulsion generated by each of propulsor fans 76A, 76B,which may provide a greater flexibility and a wider range of operationin, for example, activating a boundary layer near propulsor fans 76A,76B.

FIGS. 4A-4G are diagrams illustrating reconfiguration elements 78A-78Gconfigured to selectively transmit AC electricity from two generators totwo propulsors, in accordance with one or more techniques of thisdisclosure. For the example depicted in FIG. 4A, electrical bus 62A maybe configured to deliver a first AC electricity produced by a firstgenerator to reconfiguration element 78A. Electrical bus 62B may beconfigured to deliver a second AC electricity produced by a secondgenerator to reconfiguration element 78A.

For the example depicted in FIG. 4A, electrical bus 94 may be configuredto deliver one of the first AC electricity or the second AC electricityfrom reconfiguration element 78A to a first propulsor motor to drive afirst propulsor fan. Electrical bus 95 may be configured to deliver oneof the first AC electricity or the second AC electricity fromreconfiguration element 78A to a second propulsor motor to drive asecond propulsor fan. Reconfiguration element 78A in FIG. 4A may notconnect or refrain from connecting either of electrical busses 94, 95 toeither of electrical busses 62A, 62B.

Reconfiguration element 78B may not connect or refrain from connectingelectrical bus 94 to either of electrical busses 62A, 62B.Reconfiguration element 78B may connect electrical bus 95 to electricalbus 62B so that a second propulsor motor can drive a second propulsorfan based on a second AC electricity produced by a second generator.When electrical bus 94 is not connected to either of electrical busses62A, 62B, a first propulsor motor connected to electrical bus 94 may notdrive a first propulsor fan. A controller may cause reconfigurationelement not to transmit AC electricity to electrical bus 94 for variousreasons, such as the first propulsor motor being disabled or to produceless propulsion as compared to connecting both propulsor motors to agenerator (see reconfiguration elements 78C, 78D).

Reconfiguration element 78C may connect electrical bus 94 to electricalbus 62A so that a first propulsor motor drives a first propulsor fanbased on a first AC electricity produced by a first generator.Reconfiguration element 78C may connect electrical bus 95 to electricalbus 62B so that a second propulsor motor drives a second propulsor fanbased on a second AC electricity produced by a second generator. Thus,FIG. 4 may depict each propulsor motor of a synchronous AC electricalsystem receiving AC electricity produced by a separate generator of thesynchronous AC electrical system.

Reconfiguration element 78D may connect electrical bus 94 to electricalbus 62B so that a first propulsor motor drives a first propulsor fanbased on a second AC electricity produced by a second generator.Reconfiguration element 78D may connect electrical bus 95 to electricalbus 62A so that a second propulsor motor drives a second propulsor fanbased on a first AC electricity produced by a first generator. Thus,FIG. 4D may depict each propulsor motor of a synchronous AC electricalsystem receiving AC electricity produced by a separate generator of thesynchronous AC electrical system.

Reconfiguration element 78E may connect electrical bus 94 to electricalbus 62A so that a first propulsor motor drives a first propulsor fanbased on a first AC electricity produced by a first generator.Reconfiguration element 78E may not connect electrical bus 94 to eitherof electrical busses 62A, 62B. When electrical bus 95 is not connectedto either of electrical busses 62A, 62B, a second propulsor motorconnected to electrical bus 94 may not drive a second propulsor fan.

Reconfiguration element 78F may connect electrical bus 94 to electricalbus 62B so that a first propulsor motor drives a first propulsor fanbased on a second AC electricity produced by a second generator.Reconfiguration element 78F may connect electrical bus 95 to electricalbus 62B so that a second propulsor motor drives a second propulsor fanbased on the second AC electricity produced by the second generator.Thus, FIG. 4F may depict reconfiguration element 78F selectivelytransmitting AC electricity produced by the second generator of asynchronous AC electrical system to each propulsor motor of thesynchronous AC electrical system.

Reconfiguration element 78G may connect electrical bus 94 to electricalbus 62A so that a first propulsor motor drives a first propulsor fanbased on a first AC electricity produced by a first generator.Reconfiguration element 78G may connect electrical bus 95 to electricalbus 62A so that a second propulsor motor drives a second propulsor fanbased on the first AC electricity produced by the first generator. Thus,FIG. 4G may depict reconfiguration element 78G selectively transmittingAC electricity produced by the first generator of a synchronous ACelectrical system to each propulsor motor of the synchronous ACelectrical system. Reconfiguration elements 78A-78G may allow controller80 to switch both motors to a single generator in the case of anothergenerator being disabled. Reconfiguration elements 78A-78G may alsoprovide a wider range of operation in generating propulsion from two ormore propulsor fans.

FIGS. 5A-5C are diagrams illustrating reconfiguration elements 78H-78Kconfigured to selectively transmit AC electricity from two generators totwo propulsors, in accordance with one or more techniques of thisdisclosure. For the example depicted in FIG. 5A, electrical bus 62A maybe configured to deliver a first AC electricity produced by a firstgenerator to reconfiguration element 78H. Electrical bus 62B may beconfigured to deliver a second AC electricity produced by a secondgenerator to reconfiguration element 78H.

For the example depicted in FIG. 5A, electrical bus 94 may be configuredto deliver one of the first AC electricity or the second AC electricityfrom reconfiguration element 78H to a first propulsor motor to drive afirst propulsor fan. Electrical bus 95 may be configured to deliver oneof the first AC electricity or the second AC electricity fromreconfiguration element 78H to a second propulsor motor to drive a firstpropulsor fan. Reconfiguration element 78H in FIG. 5A may connectelectrical bus 94 to electrical bus 62A, and reconfiguration element 78Hmay connect electrical bus 95 to electrical bus 62B.

In some examples, an event may occur that causes electrical bus 62A notto deliver the first AC electricity to reconfiguration element 78H. Theevent may include a malfunction of a first turbine engine, a malfunctionof the first generator, a malfunction of electrical bus 62A, and/or anyother disabling event. As depicted in FIG. 5B, the first propulsor motormay not drive the first propulsor fan.

As depicted in FIG. 5B, reconfiguration element 78J may disconnectelectrical bus 94 from electrical bus 62A. When electrical bus 94 is notconnected to either of electrical busses 62A, 62B, a first propulsormotor connected to electrical bus 94 may not drive a first propulsorfan. As depicted in FIG. 5C, reconfiguration element 78K may connectelectrical bus 94 to electrical bus 62B so that a first propulsor motordrives a first propulsor fan based on the second AC electricity producedby the second generator, which may be unaffected by the loss of thefirst turbine engine. Thus, FIG. 5C may depict reconfiguration element78K selectively transmitting AC electricity produced by the secondgenerator of a synchronous AC electrical system to each propulsor motorof the synchronous AC electrical system. During the switch over, thefirst propulsor motor may be synchronized to the second AC electricityby windmilling and/or variation of the shaft speed of the second turbineengine. Each propulsor motor of the synchronous AC electrical system maydrive a propulsor fan despite the disabling event to electrical bus 62A.Reconfiguration elements 78H-78K may allow controller 80 to switch bothpropulsor motors to a generator in the case of the other generator beingdisabled.

FIGS. 6-8 are conceptual block diagrams illustrating engine core speedcontrol loops with combinations of fixed and variable pitch engine fansand propulsor fans, in accordance with one or more techniques of thisdisclosure. Each of synchronous AC electrical systems 110, 120, 130 mayinclude one or more engine core speed control loops. Each engine corespeed control loop may include a subtraction element Σ, an amplifier K,and an engine core, which may include an HP turbine. Subtraction elementΣ may subtract an actual value of core speed or LP speed from acommanded value of core speed or LP speed. Subtraction element Σ maygenerate an error signal based on the subtraction, an amplifier K mayamplify the error signal to generate a fuel command or a VP command. Thefuel command for the engine core may be based on the core speed. Thecore speed may drive the LP speed, which may drive the speed of apropulsor fan through a generator and a propulsor motor (not shown inFIGS. 6-8). In FIGS. 6-11, solid lines may indicate commands, and dashedlines may indicate physical connections.

FIG. 6 may depict variable-pitch (VP) commands on the propulsor fans andVP commands the engine fans, which may include an LP turbine. FIG. 7 maydepict VP commands on the engine fans, but not on the propulsor fans.FIG. 8 may depict VP commands on the propulsor fans, but not on theengine fans. The propulsor fans of synchronous AC electrical systems 120may include fixed-pitch blades, and the engine fans of synchronous ACelectrical systems 130 may include fixed-pitch blades.

For synchronous AC electrical systems 110, 130, the propulsor controllermay adjust the pitch of the variable-pitch blades of each propulsor fanin order to control the propulsion generated by each propulsor fan. Forsynchronous AC electrical systems 110, 120, the propulsor controller mayadjust the pitch of the variable-pitch blades of each engine fan inorder to control the LP speed and consequently the frequency of the ACelectricity produced by the respective generators (not shown in FIGS. 6,8). The engine core speed control loops may enable the controllers ofsynchronous AC electrical systems 110, 120, 130 to control thepropulsion generated by the propulsor fans by controlling the pitch ofthe variable-pitch blades of the engine fans and/or the propulsor fans.The control of the engine core speed may be independent of the controlof the propulsion generated by the propulsor fans.

FIGS. 9-11 are conceptual block diagrams illustrating engine LP speedcontrol loops with combinations of fixed and variable pitch engine fansand propulsor fans, in accordance with one or more techniques of thisdisclosure. Each of synchronous AC electrical systems 140, 150, 160 mayinclude one or more LP speed control loops, each of which may include anadder Σ, an amplifier K, an engine core (i.e., an HP turbine), and an LPturbine. The fuel command for the engine core may be based on the LPspeed. The core speed may drive the LP speed, which may drive the speedof a propulsor fan through a generator and a propulsor motor (not shownin FIGS. 9-11).

FIG. 9 may depict VP commands on the propulsor fans and VP commands theengine fans, which may include an LP turbine. FIG. 10 may depict VPcommands on the engine fans, but not on the propulsor fans. FIG. 11 maydepict VP commands on the propulsor fans, but not on the engine fans.The propulsor fans of synchronous AC electrical systems 150 may includefixed-pitch blades, and the engine fans of synchronous AC electricalsystems 160 may include fixed-pitch blades.

For synchronous AC electrical systems 140, 160, the propulsor controllermay adjust the pitch of the variable-pitch blades of each propulsor fanin order to control the propulsion generated by each propulsor fan. Forsynchronous AC electrical systems 140, 150, the thrust controller mayadjust the pitch of the variable-pitch blades of each engine fan inorder to control the LP speed and consequently the frequency of the ACelectricity produced by the respective generators (not shown in FIGS. 9,11).

In some examples, synchronous AC electrical systems 130, 160 may includevariable-pitch blades on the propulsor fans and fixed-pitch blades onthe engine fans. The turbine engines in synchronous AC electricalsystems 130, 160 may include fixed-pitch blades. Therefore, thefrequency of the AC electricity produced by a generator connected to afixed-pitch turbine engine may be based on the core power and the loadapplied by the propulsor fan, rather than based on the pitch of theblades of the turbine engine. Thus, the rotation of a propulsor fan maybe based on the core speed of a respective turbine engine, and acontroller may control the propulsion generated by the propulsor fan bycontrolling the pitch of the variable-pitch blades of the propulsor fan.The LP speed control loops may enable the controllers of synchronous ACelectrical systems 140, 150, 160 to control the particular frequencyproduced by the generators by controlling either the engine core speedor the pitch of the variable-pitch blades of the engine fans and/or thepropulsor fans.

FIG. 12 is a flowchart illustrating an example process 200 implementedby a system including a variable-pitch turbine engine, in accordancewith one or more techniques of this disclosure. Operations 202-208 ofprocess 200 are described in the context of synchronous AC electricalsystem 2 and controller 20 of FIG. 1.

Process 200 includes determining a propulsion for a propulsion fandriven by a propulsor motor based on a particular frequency of ACelectricity 14 for driving propulsor motor 16 (202). Controller 20 maydetermine a desired level of propulsion, i.e., thrust, from propulsorfan 18. In some examples, controller 20 may determine a desired level ofpropulsion from engine fan 7. Controller 20 may also determine theproportion of propulsion from propulsor fan 18 and engine fan 7.Controller 20 may then determine the particular frequency of ACelectricity 14 to cause propulsor motor 16 to drive propulsor fan 18 togenerate the desired propulsion. Controller 20 may then determine theparticular frequency of AC electricity 14 to cause propulsor motor 16 todrive Propulsor fan 18. Controller 20 may determine the rotational speedof shaft 10 to cause generator 12 to produce the particular frequency ofAC electricity 14. In some examples, controller 20 may sense ACelectricity 14 and the propulsion generated by propulsor fan 18 todetermine whether the current frequency of AC electricity is higher orlower than the particular frequency. Controller 20 may use an algorithmto determine the additional propulsion to reach the desired propulsion.

Process 200 also includes determining a pitch of one or morevariable-pitch blades 8A-8N of engine fan 7 of turbine engine 4 to causeshaft 10 of turbine engine 4 to rotate at a rotational speed to causegenerator 12 to produce the particular frequency of AC electricity 14(204). The rotational speed of shaft 10 may be based on the pitch ofvariable-pitch blades 8A-8N. Controller 20 may use an algorithm todetermine the pitch of variable-pitch blades 8A-8N that will result inpropulsor fan 18 to generate the desired propulsion. In some examples,controller 20 may determine the pitch that will increase the sensedpropulsion to the desired propulsion.

Process 200 also includes controlling the pitch of variable-pitch blades8A-8N of turbine engine 4 to cause generator 12 to produce ACelectricity 14 at the particular frequency (206). By controlling thepitch of variable-pitch blades 8A-8N, controller 20 may also causepropulsor motor 16 to drive propulsor fan 18 to generate the propulsionbased on AC electricity 14. Controller 20 may transmit a command to avariable-pitch unit to control the pitch of variable-pitch blades 8A-8N.Turbine engine 4 may rotate shaft 10 based on the pitch ofvariable-pitch blades 8A-8N and the fluid passing through turbine engine4. Generator 12 may produce AC electricity 14 with a particularfrequency based on a rotation of shaft 10. For example, to increase thefrequency of AC electricity 14, controller 20 may increase the pitch ofvariable-pitch blades 8A-8N in order to increase the rotational speed ofshaft 10.

Controller 20 may enable a reconfiguration element to deliver theparticular frequency of AC electricity 14 to drive the propulsor motor16 (206). Controller 20 may cause the reconfiguration element, such asreconfiguration element 44 in FIG. 2 or reconfiguration element 78 inFIGS. 3-5C, to electrically connect generator 12 to propulsor motor 16.Propulsor motor 16 may receive AC electricity 14 with the particularfrequency of AC electricity 14 produced by generator 12. The particularfrequency of AC electricity 14 may be based on the pitch ofvariable-pitch blades 8A-8N of a turbine engine 4. Propulsor motor 16may drive propulsor fan 18 to generate propulsion that is based on theparticular frequency of AC electricity 14.

FIG. 12 has described the operation of synchronous AC electrical system2 in general. In some examples, synchronous AC electrical system 2 mayinclude more than one turbine engine, more than one generator, and morethan one propulsor fan. Synchronous AC electrical system 2 may alsoinclude a reconfiguration element to selectively transmit the ACelectricity from one or more generators to one or more propulsor motors.Using the reconfiguration element, synchronous AC electrical system 2may control the propulsion at each propulsor fan and may respond todisabled turbine engines and disabled generators by switching apropulsor fan to a functioning generator.

The following numbered examples demonstrate one or more aspects of thedisclosure.

Example 1. A system includes a turbine engine including an engine fanincluding one or more variable-pitch blades driven by a shaft, whichrotates at a rotational speed which depends on a pitch of the one ormore variable-pitch blades of the engine fan. The system furtherincludes a generator configured to produce alternating-current (AC)electricity at a particular frequency relative to the rotational speedof the shaft. The system further includes a propulsor, which includes apropulsor motor and a propulsor fan. The propulsor motor is configuredto drive the propulsor fan, based on the AC electricity produced by thegenerator. The system includes a controller configured to control theparticular frequency of the AC electricity by at least controlling thepitch of the one or more variable-pitch blades of the engine fan andthereby the rotational speed of the generator.

Example 2. The system of example 1, wherein the propulsor fan comprisesone or more variable-pitch blades; and the controller is furtherconfigured to control a propulsion of the propulsor fan by at leastcontrolling a pitch of the one or more variable-pitch blades of thepropulsor fan.

Example 3. The system of examples 1 or 2 or any combination thereof,wherein the propulsor fan comprises one or more fixed-pitch blades; andthe controller is further configured to control a propulsion of thepropulsor fan by at least controlling the pitch of the one or morevariable-pitch blades of the engine fan.

Example 4. The system of examples 1-3 or any combination thereof,further including an AC electrical bus configured to transmit the ACelectricity from the generator to the propulsor motor.

Example 5. The system of examples 1-4 or any combination thereof,wherein the particular frequency of the AC electricity is based on therotation of the shaft; and the rotation of the shaft is based on thepitch of the one or more variable-pitch blades of the engine fan.

Example 6. The system of examples 1-5 or any combination thereof,wherein the turbine engine comprises a first turbine engine; the enginefan comprises a first engine fan; the shaft comprises a first shaft; thegenerator comprises a first generator; the AC electricity comprises afirst AC electricity; and the system further includes a second turbineengine including a second engine fan including one or morevariable-pitch blades and a second shaft configured to rotate based on apitch of the one or more variable-pitch blades of the second engine fan,and a second generator configured to produce, based on a rotation of thesecond shaft, a second AC electricity at a second frequency, wherein thepropulsor motor is further configured to drive, selectively based on thefirst AC electricity produced by the first generator or the second ACelectricity produced by the second generator, the propulsor fan, andwherein the controller is further configured to control the secondfrequency of the second AC electricity by at least controlling the pitchof the one or more variable-pitch blades of the second engine fan.

Example 7. The system of example 6, wherein the propulsor fan comprisesa first propulsor fan; the propulsor motor comprises a first propulsormotor; and the system further includes a second propulsor including asecond propulsor fan and a second propulsor motor configured to drive,selectively based on the first AC electricity produced by the firstgenerator or the second AC electricity produced by the second generator,the second propulsor fan.

Example 8. The system of example 7, wherein the controller is furtherconfigured to control the particular frequency and a phase of the firstAC electricity by at least controlling the pitch of the one or morevariable-pitch blades of the first engine fan; control the secondfrequency and a phase of the second AC electricity by at leastcontrolling the pitch of the one or more variable-pitch blades of thesecond engine fan, wherein the particular frequency of the first ACelectricity is equal to the second frequency of the second ACelectricity; and the phase of the first AC electricity is equal to thephase of the second AC electricity.

Example 9. The system of examples 7 or 8 or any combination thereof,further including a reconfiguration element, wherein the controller isfurther configured to cause the reconfiguration element to transmit thefirst AC electricity to zero, one, or both of the first propulsor motorand the second propulsor motor; and cause the reconfiguration element totransmit the second AC electricity to zero, one, or both of the firstpropulsor motor and the second propulsor motor.

Example 10. A method for generating propulsion, the method includingdetermining a propulsion for a propulsion fan driven by a propulsormotor based on a particular frequency of alternating-current (AC)electricity; determining a pitch of one or more variable-pitch blades ofan engine fan of a turbine engine to cause a shaft of the turbine engineto rotate at a rotational speed to cause a generator to produce theparticular frequency of AC electricity; controlling the pitch of the oneor more variable-pitch blades to cause the generator to produce the ACelectricity at the particular frequency and the propulsor motor to drivethe propulsor fan to generate the propulsion based on the ACelectricity.

Example 11. The method of example 10, further including controlling apropulsion of the propulsor fan by at least controlling a pitch of oneor more variable-pitch blades of the propulsor fan.

Example 12. The method of examples 10-11 or any combination thereof,further including enabling a reconfiguration element to deliver theparticular frequency of the AC electricity to drive the propulsor motor.

Example 13. The method of examples 10-12 or any combination thereof,further comprising determining the particular frequency of the ACelectricity based on the propulsion; determining the rotational speed ofthe shaft based on the particular frequency of the AC electricity,wherein determining the pitch of the one or more variable-pitch bladesof the engine fan is based on the rotational speed.

Example 14. The method of examples 10-13 or any combination thereof,wherein the turbine engine comprises a first turbine engine, the methodfurther including determining a second pitch of one or morevariable-pitch blades of a second engine fan of a second turbine engineto cause a second shaft of the second turbine engine to rotate at asecond rotational speed to cause a second generator to produce a secondfrequency of a second AC electricity; and controlling the second pitchof one or more variable-pitch blades of the second engine fan to cause asecond generator to produce the second AC electricity at the secondfrequency. The method further includes enabling a reconfigurationelement to selectively deliver the particular frequency of the first ACelectricity or the second frequency of the second AC electricity todrive the propulsor motor, wherein the propulsor motor is configured todrive, selectively based on the first AC electricity produced by thefirst generator or the second AC electricity produced by the secondgenerator, the propulsor fan.

Example 15. The method of example 14, further including enabling thereconfiguration element to selectively deliver the second frequency ofthe second AC electricity to drive a second propulsor motor, wherein thesecond propulsor motor is configured to drive, based on the second ACelectricity, a second propulsor fan.

Example 16. The method of examples 14 or 15 or any combination thereof,further comprising controlling the pitch of the one or morevariable-pitch blades of the engine fan of the first turbine engine andthe pitch of the one or more variable-pitch blades of the second enginefan to cause the particular frequency of the first AC electricity to beequal to the second frequency of the second AC electricity; and a phaseof the first AC electricity to be equal to a phase of the second ACelectricity.

Example 17. The method of examples 15 or 16 or any combination thereof,further including enabling the reconfiguration element to selectivelydeliver the particular frequency of the first AC electricity to zero,one, or both of the first propulsor motor and the second propulsormotor; and enabling the reconfiguration element to selectively deliverthe second frequency of the second AC electricity to zero, one, or bothof the first propulsor motor and the second propulsor motor.

Example 18. A system including a first turbine engine including a firstengine fan including one or more variable-pitch blades and a first shaftconfigured to rotate based on a pitch of the one or more variable-pitchblades of the first engine fan. The system also includes a firstgenerator configured to produce, based on a rotation of the first shaft,first alternating-current (AC) electricity at a first frequency. Thesystem further includes a second turbine engine including a secondengine fan including one or more variable-pitch blades and a secondshaft configured to rotate based on a pitch of the one or morevariable-pitch blades of the second engine fan. The system may alsoinclude a second generator configured to produce, based on a rotation ofthe second shaft, second alternating-current (AC) electricity at asecond frequency. The system further includes a propulsor including apropulsor fan and a propulsor motor configured to drive, selectivelybased on the first AC electricity produced by the first generator or thesecond AC electricity produced by the second generator, the propulsorfan. The system includes a controller configured to control the firstfrequency of the AC electricity by at least controlling the pitch of theone or more variable-pitch blades of the first engine fan, and controlthe second frequency of the AC electricity by at least controlling thepitch of the one or more variable-pitch blades of the second engine fan.

Example 19. The system of example 18, further including areconfiguration element, wherein the controller is further configured toselectively cause the reconfiguration element to transmit the first ACelectricity or the second AC electricity to the propulsor motor. Thecontroller is further configured to control a propulsion of thepropulsor fan by at least controlling a pitch of the one or morevariable-pitch blades of the first engine fan or controlling a pitch ofthe one or more variable-pitch blades of the second engine fan.

Example 20. The system of example 19, wherein the propulsor fancomprises a first propulsor fan, and the propulsor motor comprises afirst propulsor motor. The system further comprises a second propulsorincluding a second propulsor fan and a second propulsor motor configuredto drive, selectively based on the first AC electricity produced by thefirst generator or the second AC electricity produced by the secondgenerator, the second propulsor fan. The controller is furtherconfigured to selectively cause the reconfiguration element to transmitthe first AC electricity or the second AC electricity to the secondpropulsor motor, and control a propulsion of the second propulsor fan byat least controlling a pitch of the one or more variable-pitch blades ofthe first engine fan or controlling a pitch of the one or morevariable-pitch blades of the second engine fan.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A system comprising: a turbine engine includingan engine fan including one or more variable-pitch blades driven by ashaft, which rotates at a rotational speed which depends on a pitch ofthe one or more variable-pitch blades of the engine fan; a generatorconfigured to produce alternating-current (AC) electricity at aparticular frequency relative to the rotational speed of the shaft; afirst propulsor, which comprises a first propulsor motor and a firstpropulsor fan, wherein the first propulsor motor is configured to drivethe first propulsor fan, based on the AC electricity produced by thegenerator; a second propulsor, which comprises a second propulsor motorand a second propulsor fan, wherein the second propulsor motor isconfigured to drive the second propulsor fan, based on the ACelectricity produced by the generator; a reconfiguration element; and acontroller configured to: control the particular frequency of the ACelectricity by at least controlling the pitch of the one or morevariable-pitch blades of the engine fan and thereby rotational speed ofthe generator; and cause the reconfiguration element to transmit the ACelectricity to zero, one, or both of the first propulsor motor and thesecond propulsor motor.
 2. The system of claim 1, wherein: the one ormore variable-pitch blades of the engine fan are a first set of one ormore variable-pitch blades; the first propulsor fan comprises a secondset of one or more variable-pitch blades; and the controller is furtherconfigured to control a propulsion of the first propulsor fan by atleast controlling a pitch of the second set of one or morevariable-pitch blades of the first propulsor fan.
 3. The system of claim1, wherein: the first propulsor fan comprises one or more fixed-pitchblades; and the controller is further configured to control a propulsionof the first propulsor fan by at least controlling the pitch of the oneor more variable-pitch blades of the engine fan.
 4. The system of claim1, further comprising an AC electrical bus configured to transmit the ACelectricity from the generator to the first propulsor motor.
 5. Thesystem of claim 1, wherein: the particular frequency of the ACelectricity is based on the rotation of the shaft; and the rotation ofthe shaft is based on the pitch of the one or more variable-pitch bladesof the engine fan.
 6. The system of claim 1, wherein: the turbine enginecomprises a first turbine engine; the engine fan comprises a firstengine fan including a first set of the one or more variable-pitchblades; the shaft comprises a first shaft; the generator comprises afirst generator; the AC electricity comprises a first AC electricity;and the system further comprises: a second turbine engine including asecond engine fan including a second set of one or more variable-pitchblades and a second shaft configured to rotate based on a pitch of thesecond set of one or more variable-pitch blades of the second enginefan, and a second generator configured to produce, based on a rotationof the second shaft, a second AC electricity at a second frequency,wherein the first propulsor motor is further configured to drive,selectively based on the first AC electricity produced by the firstgenerator or the second AC electricity produced by the second generator,the first propulsor fan, wherein the second propulsor motor is furtherconfigured to drive, selectively based on the first AC electricity orthe second AC electricity, the second propulsor fan, and wherein thecontroller is further configured to control the second frequency of thesecond AC electricity by at least controlling the pitch of the secondset of one or more variable-pitch blades of the second engine fan. 7.The system of claim 6, wherein the controller is further configured tocause the reconfiguration element to transmit the second AC electricityto zero, one, or both of the first propulsor motor and the secondpropulsor motor.
 8. The system of claim 6, wherein the controller isfurther configured to: control the particular frequency and a phase ofthe first AC electricity by at least controlling the pitch of the firstset of one or more variable-pitch blades of the first engine fan;control the second frequency and a phase of the second AC electricity byat least controlling the pitch of the second set of one or morevariable-pitch blades of the second engine fan, wherein: the particularfrequency of the first AC electricity is equal to the second frequencyof the second AC electricity; and the phase of the first AC electricityis equal to the phase of the second AC electricity.
 9. The system ofclaim 6, wherein the controller is configured to: determine that thereconfiguration element is not receiving the first AC electricity; andcause the reconfiguration element to transmit the second AC electricityto the first propulsor motor and the second propulsor motor in responseto determining that the reconfiguration element is not receiving thefirst AC electricity.
 10. The system of claim 1, wherein thereconfiguration element comprises one or more metal-oxide semiconductorfield-effect transistors (MOSFETs), insulated-gate bipolar transistors(IGBTs), or mechanical interrupters.
 11. A method for generatingpropulsion, the method comprising: determining a target level ofpropulsion for a first propulsor fan driven by a first propulsor motorbased on a particular frequency of alternating-current (AC) electricity;determining a target of a pitch of one or more variable-pitch blades ofan engine fan of a turbine engine to cause a shaft of the turbine engineto rotate at a rotational speed to cause a generator to produce theparticular frequency of AC electricity and to cause the first propulsorfan to generate the target level of propulsion; controlling the pitch ofthe one or more variable-pitch blades to cause: the generator to producethe AC electricity at the particular frequency, and the first propulsormotor to drive the first propulsor fan to generate the target level ofpropulsion based on the AC electricity; and enabling a reconfigurationelement to selectively deliver the particular frequency of the ACelectricity to zero, one, or both of the first propulsor motor and asecond propulsor motor, wherein the second propulsor motor is configuredto drive, based on the AC electricity, a second propulsor fan.
 12. Themethod of claim 11, further comprising controlling a propulsion of thefirst propulsor fan by at least controlling a pitch of one or morevariable-pitch blades of the first propulsor fan.
 13. The method ofclaim 11, further comprising enabling the reconfiguration element todeliver the particular frequency of the AC electricity to drive thefirst propulsor motor.
 14. The method of claim 11, further comprising:determining the particular frequency of the AC electricity based on thetarget level of propulsion; determining the rotational speed of theshaft based on the particular frequency of the AC electricity, whereindetermining the target of the pitch of the one or more variable-pitchblades of the engine fan is based on the rotational speed.
 15. Themethod of claim 11, wherein the turbine engine comprises a first turbineengine, the engine fan is a first engine fan including a first set ofthe one or more variable-pitch blades, the shaft is a first shaft, thegenerator is a first generator, and the AC electricity is a first ACelectricity, the method further comprising: determining a second pitchof a second set of one or more variable-pitch blades of a second enginefan of a second turbine engine to cause a second shaft of the secondturbine engine to rotate at a second rotational speed to cause a secondgenerator to produce a second frequency of a second AC electricity;controlling the second pitch of the second set of one or morevariable-pitch blades of the second engine fan to cause the secondgenerator to produce the second AC electricity at the second frequency;enabling the reconfiguration element to selectively deliver theparticular frequency of the first AC electricity or the second frequencyof the second AC electricity to drive the first propulsor motor, whereinthe first propulsor motor is configured to drive, selectively based onthe first AC electricity produced by the first generator or the secondAC electricity produced by the second generator, the first propulsorfan; and enabling the reconfiguration element to selectively deliver thefirst particular frequency of the first AC electricity or the secondfrequency of the second AC electricity to drive the second propulsormotor, wherein the second propulsor motor is configured to drive, basedon the second AC electricity, the second propulsor fan.
 16. The methodof claim 15, further comprising controlling the pitch of the first setof one or more variable-pitch blades of the first engine fan of thefirst turbine engine and the pitch of the second set of one or morevariable-pitch blades of the second engine fan to cause: the particularfrequency of the first AC electricity to be equal to the secondfrequency of the second AC electricity; and a phase of the first ACelectricity to be equal to a phase of the second AC electricity.
 17. Themethod of claim 15, further comprising: enabling the reconfigurationelement to selectively deliver the particular frequency of the first ACelectricity to zero, one, or both of the first propulsor motor and thesecond propulsor motor; and enabling the reconfiguration element toselectively deliver the second frequency of the second AC electricity tozero, one, or both of the first propulsor motor and the second propulsormotor.
 18. The method of claim 15, further comprising: determining thatthe reconfiguration element is not receiving the first AC electricity;and causing the reconfiguration element to transmit the second ACelectricity to the first propulsor motor and the second propulsor motorin response to determining that the reconfiguration element is notreceiving the first AC electricity.
 19. A system comprising: a firstturbine engine including a first engine fan including a first set of oneor more variable-pitch blades and a first shaft configured to rotatebased on a pitch of the first set of one or more variable-pitch bladesof the first engine fan; a first generator configured to produce, basedon a rotation of the first shaft, first alternating-current (AC)electricity at a first frequency; a second turbine engine including asecond engine fan including a second set of one or more variable-pitchblades and a second shaft configured to rotate based on a pitch of thesecond set of one or more variable-pitch blades of the second enginefan; a second generator configured to produce, based on a rotation ofthe second shaft, second alternating-current (AC) electricity at asecond frequency; a propulsor including a propulsor fan and a propulsormotor configured to drive, selectively based on the first AC electricityproduced by the first generator or the second AC electricity produced bythe second generator, the propulsor fan; a reconfiguration element; anda controller configured to: control the first frequency of the ACelectricity by at least controlling the pitch of the first set of theone or more variable-pitch blades of the first engine fan; control thesecond frequency of the AC electricity by at least controlling the pitchof the second set of the one or more variable-pitch blades of the secondengine fan; selectively cause the reconfiguration element to transmitthe first AC electricity or the second AC electricity to the firstpropulsor motor; and control a propulsion of the propulsor fan by atleast controlling the pitch of the first set of the one or morevariable-pitch blades of the first engine fan or controlling the pitchof the second set of the one or more variable-pitch blades of the secondengine fan.
 20. The system of claim 19, wherein the controller isfurther configured to: determine that the reconfiguration element is notreceiving the first AC electricity; and cause the reconfigurationelement to transmit the second AC electricity to the propulsor motor inresponse to determining that the reconfiguration element is notreceiving the first AC electricity.